An usher said Tuesday he was chatting with abortion doctor George Tiller in church when he was gunned down and killed.
Gary Hoepner testified at accused shooter Scott Roeder's preliminary hearing that he and Tiller were making small talk May 31 when he saw a man come through a church door and put a gun to Tiller's head.
He then heard a shot and saw Tiller go down.
"George fell to the ground and I just said in my mind 'oh my God,'" he told a Kansas courtroom. Hoepner, the prosecution's first witness, said he didn't know whether the weapon was a "cap gun" or a real pistol.
Roeder, 51, pleaded not guilty at the hearing later Tuesday. He was dressed in a jacket and tie, and fidgeted and yawned during testimony.
Among those on the potential witness list at his preliminary hearing is a woman convicted of shooting Tiller in the arms in 1993.
Rachelle "Shelley" Shannon was found guilty of opening fire on the late-term abortion provider as the doctor drove away from his Wichita clinic, wounding him.
Roeder, of Kansas City, Mo., is accused of shooting and killing Tiller while the doctor served as an usher at the Wichita church he regularly attended.
Authorities also claim Roeder threatened two ushers, including Hoepner, who tried to stop him during the attack in the building's foyer.
"'I've got a gun and I'll shoot you,"' Hoepner recalled Roeder saying. "I believed him and I stopped."
He said during his 90-minute testimony that he followed the shooter, who he identified as Roeder, out of the church but stopped after Roeder warned him.
He said he later called police to give them the license plate number on the shooter's car.
Defense attorney Steve Osburn said some of Hoepner's testimony was based on assumptions, including whether the gunman spoke directly to the other usher.
Osburn also asked Hoepner if he told police he heard the gunman say something along the line of "Lord, Forgive me."
Hoepner said he did.
Another member of Tiller's church testified that he was able to get the license plate on the alleged gunman's car before he sped away.
Thornton Anderson said he heard a "commotion" in the church parking lot, and a man yelled for him to get the license plate of a car that was driving near him.
Anderson, the day's second witness, said he "clearly observed" the car's license plate because "I'm a numbers guy."
Most of those on tap to testify Tuesday against Roeder are law enforcement officials, though it wasn't known how many of the more than 200 witnesses the government plans to bring to the stand.
On the list are members of the anti-abortion group Operation Rescue; Roeder's ex-wife and son; and Tiller's wife, Jeanne, who was singing in the choir when her husband was shot.
Prosecutors must convince a judge they have enough evidence to merit a trial on one count of first-degree murder and two counts of aggravated assault.
Tiller, 67, had been the target of regular protests for most of the 36 years he performed abortions at his Wichita clinic, where he practiced as one of the nation's few providers of late-term abortions. The doctor had been repeatedly threatened over the years.
If Roeder is convicted of first-degree murder, he faces life in prison with the possibility of parole after 25 years.
In rambling jailhouse interviews, Roeder has talked about the notion of justifiable homicide against abortion providers, but he has refused to discuss any facts of his case.
Roeder has told The Associated Press Tiller's shooting was justified, but never has claimed a role in the slaying.
The Associated Press contributed to this report.